This invention relates to seismic exploration and more particularly to marine exploration. In marine exploration, seismic energy is generated in the water and reflections of such energy from subsurface interfaces are detected by a linear string of detectors or hydrophones. The seismic energy sources and the detectors are towed through the water by means of cables extending from a marine vessel. Signals received by the detectors are transferred to the vessel through the cable wiring. In many instances, groups of detectors are combined to form arrays within the cable, and the signals received by each such array are combined and transferred to the vessel.
One method for determining the instantaneous position of each detector or array of detectors along the cable as the cable is towed through the water is disclosed in U.S. Pat. No. 3,953,827 to Le Moal et al. A plurality of detectors or hydrophones are distributed along a towed cable. The position of each detector is determined by the interpolation of values of the angle of the tangents to the cable with a fixed and known direction, such as magnetic north, at a plurality of measuring points. At each measuring point along the cable there is located preferably a magnetic compass. There is also provided means for coding and transmitting the measured values by means of electronic pulses to a central station. Such means includes a multiplex device. The position of each measuring point is determined by assimilating that part of the towed cable located between compasses to an arc of a circle, the length of which is known from the construction of the cable, while the angular value of the arc is determined from the differences between the angles measured by the compasses between the tangent to the cable and the fixed and known direction. The positions of the detectors along the cable are then determined by interpolation between the positions of the compasses along the cable.